1. Field of the Invention
The present invention relates to a synchronization system and method for databases, and more particularly to a system and a method for synchronizing a database of an information terminal connected to the Internet through a packet communication line and another database of an application server connected normally to the Internet with each other.
2. Description of the Related Art
Conventionally, in a synchronization system and method for databases of the type described, if it is tried to start synchronization from the information terminal side, then it is necessary for the information terminal to perform dialup connection to a service provider on the Internet to establish a connection between applications and communicate data with the database of the application server to establish synchronism.
Also when it is tried to establish synchronism from the application server side normally connected to the Internet, the application server performs dialup connection to a telephone circuit connected to the information terminal through the service provider to establish a connection to the information terminal to establish a connection between the applications to establish synchronism.
Recently, such a new service as described below has become available. In particular, referring to FIG. 11, a mail server 1 on the service provider side and a personal computer 2 of the user side are connected to an ISDN network 5 through terminal adapters 3 and 4 provided therefor, respectively. According to the new service, if an electronic mail destined for the user arrives at the mail server 1 of the service provider, then the termination information is transmitted to the terminal adapter 4 of the user side using a D channel packet of the ISDN network.
The conventional system, however, has the following disadvantages.
The first disadvantage resides in that, in order to establish synchronism between the database of the application server and the database of the information terminal, dialup connection by a telephone circuit is required. For the immediacy of synchronization between the databases, dialup connection must be performed every time data of the databases are updated, and this requires a corresponding cost. On the other hand, in order to suppress the cost, synchronism is established after data are updated several times, and this makes the updating period long.
The second disadvantage resides in that the power supply to the information terminal is normally on. This is because, although the power supply to the information terminal must be on naturally when an operation for synchronization is performed from the information terminal side, also when it is tried to establish synchronism from the application server side, the information terminal must accept dialup connection, and therefore, when an operation for synchronization is to be performed, the information terminal must always be in a standby state with the power supply thereto kept on.
Japanese Patent Laid-Open No. 2000-76218 discloses a synchronization system which allows synchronization between databases with a firewall interposed therebetween. The synchronization system includes an internal database server including an internal database and provided in a firewall, and an external database server including an external database and provided outside the firewall. The internal database server includes an internal differential data extraction section for extracting internal differential data updated within a predetermined period as internal data from among data possessed by the external database. Meanwhile, the external database server includes an external differential data extraction section for extracting external differential data updated within a predetermined period as external data from data possessed by the external database. The internal database server further includes an internal time storage section for storing a start time of a predetermined period with regard to the internal differential data, and an internal data updating confirmation section for confirming whether or not the external database has been updated with the internal differential data. Meanwhile, the external database server further includes an external time storage section for storing a start time of a predetermined period with regard to the external differential data, and an external data updating confirmation section for conforming whether or not the internal database has been updated with the external differential data. If the internal data updating confirmation section confirms that the external database has been updated with the internal differential data, then the internal time storage section updates the start time with regard to the internal differential data. Meanwhile, if the external data updating confirmation section confirms that the internal database has been updated with the external differential data, then the external time storage section updates the start time with regard to the external differential data.
However, also with the synchronization system just described, the power supply to the internal database server must always be on.